1. Field of the Invention
This invention relates to keyboard assemblies which are used for electronic keyboard instruments such as electronic organs, electronic pianos and synthesizers. This application is based on patent application No. Hei 9-41060, patent application No. Hei 9-41066 and patent application No. Hei 9-54264 all filed in Japan, the contents of which are incorporated herein by reference.
2. Prior Art
As the keyboard assemblies used for the electronic keyboard instruments, the paper of Japanese Patent Laid-Open Publication No. 6-342281 discloses an example of the comb-tooth-type keyboard unit.
The typical construction of the comb-tooth-type keyboard unit will be simply described in conjunction with FIG. 14. FIG. 14 is an exploded perspective view for an assembly of three key units, i.e., two white key units 1, 1' and one black key unit 1".
The white key unit 1 contains multiple keys each denoted by a numeral "2", which are supported by a key support (or key common support) 3. The key support 3 extends in a direction of arrangement of keys (hereinafter, simply referred to as key-arrangement direction). A connection (or supporting point) 4, whose width is equivalent to that of a back end 2a of the key 2, connects the key 2 to the key support 3 to provide flexibility that the key 2 can be freely swung up and down in key-depression-release directions A. The aforementioned elements 2, 3 and 4 are formed as integral parts using resin to construct the white key unit 1.
The white key unit 1' and the black key unit 1" are constructed as similar to the aforementioned white key unit 1. Herein, a numeral 3' designates a key support of the white key unit 1' while a numeral 3" designates a key support of the black key unit 1". The key support 3 of the white key unit 1 is placed upon the key support 3' of the white key unit 1'. In addition, the key support 3" of the black key unit 1" is further placed upon the key support 1 of the white key unit 1. So, the three key units are assembled together and are securely fixed to a main frame (not shown) by screws.
For convenience' sake, FIG. 14 provides an illustration such that each of the key units has two keys. Actually, however, the white key unit 1' has four keys corresponding to notes C, E, G and B respectively; the white key unit 1 has three keys corresponding to notes D, F and A respectively; and the black key unit 1" has five keys corresponding to notes C#, D#, E#, G# and A# respectively. The above keys are assembled together to form a keyboard unit of one octave.
A number of keyboard units (each of which is not necessarily limited to the keyboard unit of one octave) are arranged in a key-arrangement direction and are securely fixed to a base (not shown) by screws. Thus, it is possible to construct a keyboard unit having a certain number of keys, such as C37 scale and C49 scale.
Suppose that the keyboard unit of FIG. 14 containing the white key unit 1' and the black key unit 1" is arranged adjacent to a keyboard unit (not shown) containing a white key unit 1'-x and a black key unit 1"-x. Herein, the key support 3' of the white key unit 1' is defined by two ends 3a' and 3b' while a key support 3'-x of the adjacent white key unit 1'-x is defined by two ends 3a'-x and 3b'-x; and the key support 3" of the black key unit 1" is defined by two ends 3a" and 3b" while a key support 3"-x of the adjacent black key unit 1"-x is defined by two ends 3a"-x and 3b"-x. In this case, the white key unit 1' is placed to partially overlap with the adjacent white key unit 1'-x in such a way that the first end 3a' of the key support 3' overlaps with the second end 3b'-x of the key support 3'-x, while the black key unit 1" is placed to partially overlap with the adjacent black key unit 1"-x in such a way that the first end 3a" of the key support 3" overlaps with the second end 3b"-x of the key support 3"-x. Screws are inserted into screw holes of the above key supports as shown by dashed lines in FIG. 14, so the key supports are securely fixed to the base of the main frame (not shown) by screws. Thus, it is possible to mutually interconnect the adjacent key units together with certain positioning.
A keyboard circuit board on which key switches are mounted for keys respectively is provided beneath the keyboard unit.
The aforementioned keyboard unit does not require the mechanical process with respect to the supporting points and frame. In addition, multiple keys are formed integrally as a unit. Therefore, the keyboard unit has a small number of parts, so it is possible to perform construction and maintenance of the keyboard unit with ease. Further, the aforementioned construction of the keyboard unit is very effective in reduction of manufacturing cost.
The aforementioned example of the comb-tooth-type keyboard unit is constructed using the foregoing key units such that ends of the key supports of the adjacent key units are placed to overlap with each other and are tightly fixed each other using fasteners such as screws. In the case of the repairs and maintenance of the keyboard circuit board and the like, it is necessary to remove the key unit arbitrarily selected from the base. In such case, it is impossible to remove the key unit by merely loosening the fasteners. In other words, it is necessary to sequentially remove the key units in accordance with an order of the key-arrangement direction which starts from the key unit having the key of the lowest pitch or the key unit having the key of the highest pitch. So, the aforementioned keyboard unit has a problem that a work efficiency for disassembling is not so good.
At positioning of the key units, projections for positioning are provided to engage with holes to make a gap between adjacent keys constant. Or, a gap between adjacent keys is adjusted manually. So, there is another problem that a work efficiency for positioning is not so good, so gaps become irregular with ease.
The paper of Japanese Patent Laid-Open Publication No. 7-92963 discloses another example of the comb-tooth-type keyboard unit, which is characterized by excluding key guides.
FIG. 15 shows a selected part of a key unit of the keyboard unit. Herein, a key unit 1 has two keys each denoted by a same numeral "2". The keys 2 are connected to a key support 3 by connections 4. A through hole 5 is formed to cut an intermediate part of each connection 4, while each connection 4 has a sufficient degree of flexibility in key-depression-release directions. In addition, each connection 4 has a width "W" in a key-width direction, which is broader than a width "a" of a back end of each key 2. Like the aforementioned keyboard unit of FIG. 14, the keyboard unit of FIG. 15 is constructed by assembling white key units and black key units together to partially overlap with each other. Herein, a connection of a key of one key unit partially overlaps with a connection of an adjacent key of another key unit in a plane with a small gap.
By making the width of the connection 4 to be broader than the width "a" of the back end of the key 2, a second moment of area becomes large with respect to the key-width direction of the connection 4. So, it is possible to sufficiently regulate the lateral swing (i.e., yawing) of the key 2 in the key-width direction without using key guides. Thus, it is possible to manufacture the keyboard unit, which does not have difficulty in playing the performance technique of glissando, with low cost.
In the manufacturing of the conventional keyboard units, at formation of the key unit using the resin, the resin material is provided from the gate of the metal mold to a position corresponding to a side portion of the key(s). This causes an unbalance in flow of the resin material in the metal mold. In some case, the resin material solidifies in a distorted manner, which increases the residual stress of the key unit formed by the resin. For this reason, there is a problem the durability of the key unit is deteriorated. Reduction of the durability occurs particularly around the gate of the metal mold and/or the weld line at which flows of the resin material join together.
Due to the existence of the gate-corresponding portion of the key into which the resin material is put, it may be necessary to provide a long distance for the resin material to flow toward the key support 3. So, the weld line is formed along the connection, which causes a possibility that the durability of the key unit is reduced. The connection act as a hinge, by which the key is connected to the key support such that the key is capable of swinging up and down in key-depression-release directions. So, the connection is formed to have a thin wall. In addition, the force of flexure is frequently applied to the connection, so there is a possibility that the connection is destructed with ease. Due to uneven support intensity, performance feeling (or touch feeling) of the key becomes uneven, so performability of the key is deteriorated.
In the case of the keyboard unit of FIG. 15 that the width of the connection is broadened while the through hole is formed at the intermediate part of the connection, an unbalance state occurs in flow of the resin material with respect to the left side and right side of the connection. This makes the durability of the key unit to be further deteriorated.
Another type of the keyboard unit is constructed by assembling an upper case with a lower case where keys are mounted. In this type of the keyboard unit, bosses are formed to project on the lower case, so a key frame attached to the bosses supports each of keys to have a capability of freely swinging up and down. A keyboard circuit board is attached to a surface of the key frame such that it faces with the keys. Key switches are mounted on the keyboard circuit board to detect key-depression operations of the keys.
A main circuit board on which a sound source circuit and other circuit components are mounted is attached to a back portion of the lower case which is provided backwardly from the key frame.
Connectors are provided for the keyboard circuit board and main circuit board respectively. The connectors are electrically connected by a flat cable. So, a key-on signal produced by a key switch is transmitted to the sound source circuit on the main circuit board via the flat cable.
The flat cable is wired using a space between the key frame and lower case or spaces located at left and right ends of the lower case.
When wiring the flat cable, the above space (or spaces) should be secured in proximity to the lower case or inside of the lower case. Provision of the above space (or spaces) interrupts the flattening and downsizing of the lower case.
In some case, the key frame is omitted so that the lower case is re-designed to directly support each of the keys to have a capability of freely swinging up and down. In that case, it is possible to flatten the lower case. However, no space is formed between the key frame and lower case. In addition, at the key depression, key-depression load of the key is directly imparted to the lower case. For this reason, it is necessary to reinforce the lower case.
When wiring the cable(s) using the spaces located at the left and right ends of the lower case, the cable(s) should be elongated. Thus, the engineer should make a consideration on the noise resistance. In addition, it is necessary to draw in the flat cable toward the left and right ends of the lower cable. So, it is necessary to perform troublesome wiring work.
As described above, the keyboard unit is required to have a lower case which is subjected to flattening and downsizing. Herein, it is demanded that the keyboard unit is designed to have a capability of easy wiring of the cable providing connection between the keyboard circuit board and main circuit board.
Further, it is demanded to provide a keyboard unit whose lower case, which is easily deformed by load(s) because of the flattening, can be reinforced.